This invention relates to a method and apparatus for removing ballast and the like from beneath a railroad track and more particularly to undercutters and trench digging means used in combination to remove ballast and other material from beneath the ties of the track.
As is well known, it often becomes necessary to remove existing ballast from beneath a railroad track and replace it with fresh ballast. It is also occasionally necessary to remove such ballast to carry out repairs on the track itself. It is preferable to remove and replace the ballast without disturbing the network of ties and rails on the track.
To this end, methods and machines, such as undercutters, have been proposed and used in the past to remove the ballast and other material from beneath the railroad ties. In general, undercutters employ a toothed chain which moves about an elongated horizontal chain guide. The chain is moved into position beneath the ties in a horizontal plane and extends parallel thereto as it operates to remove ballast and other material from beneath the ties and to transfer the same toward one side of the bed of the track. Early undercutters of the type hereinabove described were suitable for use only in areas where the railroad track and bed were elevated above the surrounding ground level or where bordering ditches provided access to the track bed beneath the ties. Furthermore, the horizontal access required for such undercutters often required the unnecessary removal of much of the roadbed alongside the track when only the ballast under the ties needed replacing.
The apparatus disclosed in U.S. Pat. No. 3,967,396 issued July 6, 1976 to Maisoneve et al served to reduce some of the above problems in that this apparatus enabled removal of ballast from beneath the track at areas which were not elevated. However, such apparatus still requires substantial disturbance to the railroad bed. The design and method of operation of this apparatus incorporates a vertically disposed rotary trencher and a horizontally disposed undercutter which has its discharge end extending within the open space in the interior of the trencher during the normal operation of the apparatus. The initial alignment of the components is parallel and side-by-side, however the horizontally disposed undercutter is rotated 90.degree. in a horizontal plane to bring it into an operative position beneath the railroad track with the discharge end thereof extending into the open space in the interior of the trencher. Due to this design the support mechanisms for the horizontally disposed undercutter and the drive mechanisms for the horizontally disposed undercutter as well as the positioning mechanisms for the undercutter are all located within the open space in the interior of the trencher. This configuration limits the size of the components which may be utilized as undercutters, supports and drive means.
In order to position the undercutter beneath the railroad ties it is necessary to dig two trenches adjacent the railroad ties: one for the trencher and one for ingress and egress of the undercutter. When the undercutter has been thus positioned beneath the ties, the trencher and undercutter assembly may be moved in unison to a position such that the trencher is adjacent the end of the railroad ties. In the event of mechanical failure of the horizontal undercutter necessitating removal of the cutter blade of the undercutter from beneath the tracks, the trencher would have to be employed to excavate a sufficient volume of material extending laterally from the ends of the railroad ties to facilitate removal of the cutter blade therefrom or the railroad ties and track above the cutter blade would have to be removed. Likewise, if mechanical failure of the trencher wheel occurred during normal operation, the apparatus would be immobilized whereby it would be unable to go forward due to the inoperability of the trencher wheel, unable to go backward without damaging the ties and track if no ballast has been replaced beneath the ties and track, yet unable to go backwards if the ballast has been replaced due to the inoperability of the trencher wheel; and unable to raise the trencher wheel due to the juxtaposition of the associated undercutter within the confines of the trencher wheel and beneath the railroad tracks.